We owned a 240 and I'd have to say attaching a mainsheet to the rudder head is not advised but I think a few have attempted this. I'd agree with David and PB on the loss of a bimini with the attachment at the end of the boom and the issue of strength at the rudder head.
While I've considered a traveler as Alan recommended, the space to place one is extremely limited on a 240/260 and would create a substantial(if not impossible) impediment to moving in/out of the cabin across an already tricky step. I'm sure on a boat with a more serious approach to performance it would override the inconvenience but after using our 260 for a few years I can't imagine the gain would be worth working around the hardware at the cabin step for a few degrees upwind.
That said, Alans idea to add a traveler that can be pinned or added in a quick release bracket across the seats at the bulkhead(if there're strong enough) might make my summer haul out re-engineering to-do list. One issue would be moving the mainsheet even further away from the wheel. It all goes against my KISS rule on these casual little boats but maybe.
Here's a pic of the tight spot it'd be added in. My coffee maker would have to work around any added hardware which could be complicated if she ain't happy, creating other serious performance issues not related to boat speed.
Mike and Kelli